Traditionally, a relay may be used to extend communication range when the range of single-hop wireless communication is limited by distance or harsh radio propagation conditions. Such relays build a multi-hop path between an out-of range node and an access point. The frames are forwarded hop-by-hop from the source to the destination. However, to avoid self-interference, transmission on different hops cannot be activated simultaneously when the nodes are within direct communication range. Consequently, the decrease in throughput over multi-hop paths is inversely proportional to the number of hops between the sender and the destination. For example, in a two-hop path with a single relay, throughput from the sender to the destination is only half of the data rate compared to a single hop wireless link.
For example when a source sends four frames to a destination with a traditional multi-hop relay system using two relays, the source sends each packet to one of the relays and waits for the relay to forward the packet to the destination since the two relays can interfere with each other. Thus, typically, to send four frames requires eight time slots.